Binding phenomena between ligands and receptors play many crucial roles in biological systems. Exemplary of such phenomena are the binding of oxygen molecules to deoxyhemoglobin to form oxyhemoglobin, and the binding of a substrate to an enzyme that acts upon it such as between a protein and a protease like trypsin. Still further examples of biological binding phenomena include the binding of an antigen to an antibody 1 and the binding of complement component C3 to the so-called CR1 receptor.
Many drugs and other therapeutic agents are also believed to be dependent upon binding phenomena. For example, opiates such as morphine are reported to bind to specific receptors in the brain. Opiate agonists and antagonists are reported to compete with drugs like morphine for those binding sites.
Ligands such as man-made drugs, like morphine and its derivatives, and those that are naturally present in biological systems such as endorphins and hormones bind to receptors that are naturally present in biological systems, and will be treated together herein. Such binding can lead to a number of the phenomena of biology, including particularly the hydrolysis of amide and ester bonds as where proteins are hydrolyzed into constituent polypeptides by an enzyme such as trypsin or papain or where a fat is cleaved into glycerine and three carboxylic acids, respectively. In addition, such binding can lead to formation of amide and ester bonds in the formation of proteins and fats, as well as to the formation of carbon to carbon bonds and carbon to nitrogen bonds.
An exemplary receptor-producing system in vertebrates is the immune system. The immune system of a mammal is one of the most versatile biological systems as probably greater than 1.0×107 receptor specificities, in the form of antibodies, can be produced. Indeed, much of contemporary biological and medical research is directed toward tapping this repertoire. During the last decade there has been a dramatic increase in the ability to harness the output of the vast immunological repertoire. The development of the hybridoma methodology by Kohler and Milstein has made it possible to produce monoclonal antibodies, i.e., a composition of antibody molecules of a single specificity, from the repertoire of antibodies induced during an immune response.
Unfortunately, current methods for generating monoclonal antibodies are not capable of efficiently surveying the entire antibody response induced by a particular immunogen. In an individual animal there are at least 5-10,000 different B-cell clones capable of generating unique antibodies to a small relatively rigid immunogens, such as, for example dinitrophenol. Further, because of the process of somatic mutation during the generation of antibody diversity, essentially an unlimited number of unique antibody molecules may be generated. In contrast to this vast potential for different antibodies, current hybridoma methodologies typically yield only a few hundred different monoclonal antibodies per fusion.
Other difficulties in producing monoclonal antibodies with the hybridoma methodology include genetic instability and low production capacity of hybridoma cultures. One means by which the art has attempted to overcome these latter two problems has been to clone the immunoglobulin-producing genes from a particular hybridoma of interest into a procaryotic expression system. See, for example, Robinson et al., PCT Publication No. WO 89/0099; Winter et al., European Patent Publication No. 0239400; Reading, U.S. Pat. No. 4,714,681; and Cabilly et al., European Patent Publication No. 0125023.
The immunologic repertoire of vertebrates has recently been found to contain genes coding for immunoglobulins having catalytic activity. Tramontano et al., Sci., 234:1566-1570 (1986); Pollack et al., Sci., 234:1570-1573 (1986); Janda et al., Sci., 241:1188-1191 (1988); and Janda et al., Sci., 244:437-440 (1989). The presence of, or the ability to induce the repertoire to produce, antibodies molecules capable of a catalyzing chemical reaction, i.e., acting like enzymes, had previously been postulated almost 20 years ago by W. P. Jencks in Catalysis in Chemistry and Enzymoloqy, McGraw-Hill, N.Y. (1969).
It is believed that one reason the art failed to isolate catalytic antibodies from the immunological repertoire earlier, and its failure to isolate many to date even after their actual discovery, is the inability to screen a large portion of the repertoire for the desired activity. Another reason is believed to be the bias of currently available screening techniques, such as the hybridoma technique, towards the production high affinity antibodies inherently designed for participation in the process of neutralization, as opposed to catalysis.